To save her kingdom, a determined young mermaid princess and her friends must join forces with the creatures that scare them the most — humans.
Merlinda’s coming-of-age celebration is disrupted when an ancient force tests her courage and a dangerous enemy threatens all of Mertropia.
Back in Morton Bay, the mermaids help Celia through a surprising change - until an old enemy turns an ordinary school day into a dangerous showdown.
Merlinda and her friends enter the Morton Bay Regatta, racing above and below the waves toward a magical secret with the power to restore Mertropia.
As the search for Jelly goes on, a new lead brings Merlinda and her friends closer to the Sea Witch, only to land them in a dangerous trap.
The Sea Witch pulls Merlinda into an ancient vault beneath the waves. As her friends race to help, Merlinda searches the darkness for a way out.